The present invention relates to a family of colorants and colorant modifiers. The colorant modifiers, according to the present invention, are capable of stabilizing a color to ordinary light and/or rendering the colorant mutable when exposed to specific wavelengths of electromagnetic radiation.
A major problem with colorants is that they tend to fade when exposed to sunlight or artificial light. It is believed that most of the fading of colorants when exposed to light is due to photodegradation mechanisms. These degradation mechanisms include oxidation or reduction of the colorants depending upon the environmental conditions in which the colorant is placed. Fading of a colorant also depends upon the substrate upon which they reside.
Product analysis of stable photoproducts and intermediates has revealed several important modes of photodecomposition. These include electron ejection from the colorant, reaction with ground-state or excited singlet state oxygen, cleavage of the central carbon-phenyl ring bonds to form amino substituted benzophenones, such as triphenylmethane dyes, reduction to form the colorless leuco dyes and electron or hydrogen atom abstraction to form radical intermediates.
Various factors such as temperature, humidity, gaseous reactants, including O2, O3, SO2, and NO2, and water soluble, nonvolatile photodegradation products have been shown to influence fading of colorants. The factors that effect colorant fading appear to exhibit a certain amount of interdependence. It is due to this complex behavior that observations for the fading of a particular colorant on a particular substrate cannot be applied to colorants and substrates in general.
Under conditions of constant temperature it has been observed that an increase in the relative humidity of the atmosphere increases the fading of a colorant for a variety of colorant-substrate systems (e.g., McLaren, K., J. Soc. Dyers Colour, 1956, 72, 527). For example, as the relative humidity of the atmosphere increases, a fiber may swell because the moisture content of the fiber increases. This aids diffusion of gaseous reactants through the substrate structure.
The ability of a light source to cause photochemical change in a colorant is also dependent upon the spectral distribution of the light source, in particular the proportion of radiation of wavelengths most effective in causing a change in the colorant and the quantum yield of colorant degradation as a function of wavelength. On the basis of photochemical principles, it would be expected that light of higher energy (short wavelengths) would be more effective at causing fading than light of lower energy (long wavelengths). Studies have revealed that this is not always the case. Over 100 colorants of different classes were studied and found that generally the most unstable were faded more efficiently by visible light while those of higher lightfastness were degraded mainly by ultraviolet light (McLaren, K., J. Soc. Dyers Colour, 1956, 72, 86).
The influence of a substrate on colorant stability can be extremely important. Colorant fading may be retarded or promoted by some chemical group within the substrate. Such a group can be a ground-state species or an excited-state species. The porosity of the substrate is also an important factor in colorant stability. A high porosity can promote fading of a colorant by facilitating penetration of moisture and gaseous reactants into the substrate. A substrate may also act as a protective agent by screening the colorant from light of wavelengths capable of causing degradation.
The purity of the substrate is also an important consideration whenever the photochemistry of dyed technical polymers is considered. For example, technical-grade cotton, viscose rayon, polyethylene, polypropylene, and polyisoprene are known to contain carbonyl group impurities. These impurities absorb light of wavelengths greater than 300 nm, which are present in sunlight, and so, excitation of these impurities may lead to reactive species capable of causing colorant fading (van Beek, H. C. A., Col. Res. Appl., 1983, 8(3), 176).
Therefore, there exists a great need for methods and compositions which are capable of stabilizing a wide variety of colorants from the effects of both sunlight and artificial light.
There is also a need for colorants that can be mutated, preferably from a colored to a colorless form, when exposed to a specific predetermined wavelength of electromagnetic radiation. For certain uses, the ideal colorant would be one that is stable in ordinary light and can be mutated to a colorless form when exposed to a specific predetermined wavelength of electromagnetic radiation.
The present invention addresses the needs described above by providing compositions and methods for stabilizing colorants against radiation including radiation in the visible wavelength range. In addition, the present invention provides certain embodiments in which the light-stable colorant system is mutable by exposure to certain narrow bandwidths of radiation. In certain embodiments, the colorant system is stable in ordinary visible light and is mutable when exposed to a specific wavelength of electromagnetic radiation.
In one embodiment, the present invention provides a composition comprising a colorant which, in the presence of a radiation transorber, is mutable when exposed to a specific wavelength of radiation, while at the same time, provides light stability to the colorant when the composition is exposed to sunlight or artificial light. The radiation transorber may be any material which is adapted to absorb radiation and interact with the colorant to effect the mutation of the colorant. Generally, the radiation transorber contains a photoreactor and a wavelength-specific sensitizer. The wavelength-specific sensitizer generally absorbs radiation having a specific wavelength, and therefore a specific amount of energy, and transfers the energy to the photoreactor. It is desirable that the mutation of the colorant be irreversible.
The present invention also relates to colorant compositions having improved stability, wherein the colorant is associated with a modified photoreactor. It has been determined that conventional photoreactors, which normally contain a carbonyl group with a functional group on the carbon alpha to the carbonyl group, acquire the ability to stabilize colorants when the functional group on the alpha carbon is removed via dehydration.
Accordingly, the present invention also includes a novel method of dehydrating photoreactors that have a hydroxyl group in the alpha position to a carbonyl group. This reaction is necessary to impart the colorant stabilizing capability to the photoreactor. The novel method of dehydrating photoreactors that have a hydroxyl group in the alpha position to a carbonyl group can be used with a wide variety of photoreactors to provide the colorant stabilizing capability to the photoreactor. The resulting modified photoreactor can optionally be linked to wavelength-selective sensitizer to impart the capability of decolorizing a colorant when exposed to a predetermined narrow wavelength of electromagnetic radiation. Accordingly, the present invention provides a photoreactor capable of stabilizing a colorant that it is admixed with.
In certain embodiments of the present invention, the mixture of colorant and radiation transorber is mutable upon exposure to radiation. In this embodiment, the photoreactor may or may not be modified as described above to impart stability when admixed to a colorant. In one embodiment, an ultraviolet radiation transorber is adapted to absorb ultraviolet radiation and interact with the colorant to effect the irreversible mutation of the colorant. It is desirable that the ultraviolet radiation transorber absorb ultraviolet radiation at a wavelength of from about 4 to about 300 nanometers. It is even more desirable that the ultraviolet radiation transorber absorb ultraviolet radiation at a wavelength of 100 to 300 nanometers. The colorant in combination with the ultraviolet radiation transorber remains stable when exposed to sunlight or artificial light. If the photoreactor is modified as described above, the colorant has improved stability when exposed to sunlight or artificial light.
Another stabilizer that is considered part of the present invention is an arylketoalkene having the following general formula: 
wherein
R1 is hydrogen, an alkyl, alkenyl, cycloalkyl, heterocycloalkyl, aryl or a heteroaryl group;
R2 is hydrogen, alkyl, alkenyl, cycloalkyl, heterocycloalkyl, aryl or a heteroaryl group;
R3 is hydrogen, alkyl, alkenyl, cycloalkyl, heterocycloalkyl, aryl or a heteroaryl group; and
R4 is an aryl, heteroaryl, or substituted aryl group. Preferably, the alkene group is in the trans configuration.
Desirably, the arylketoalkene stabilizing compound has the following formula. 
which efficiently absorbs radiation having a wavelength at about 308 nanometers, or 
which efficiently absorbs radiation having a wavelength at about 280 nanometers. Desirably, arylketoalkene stabilizing compound of the present invention is in the trans configuration with respect to the double bond. However, the sensitizer may also be in the cis configuration across the double bond.
Accordingly, this embodiment of the present invention provides a stabilizing molecule, the above arylketoalkene, which when associated with a colorant, stabilizes the colorant. Therefore, the above arylketoalkene can be used as an additive to any colorant composition. For example, as the arylketoalkene compound is poorly soluble in water, it can be directly added to solvent or oil based (not water based) colorant compositions. Additionally, the arylketoalkene compound can be added to other colorant compositions that contain additives enabling the solubilization of the compound therein. Further, the arylketoalkene stabilizing compounds can be solubilized in an aqueous solution by attaching the compound to a large water soluble molecule, such as a cyclodextrin.
In another embodiment of the present invention, the colored composition of the present invention may also contain a molecular includant having a chemical structure which defines at least one cavity. The molecular includants include, but are not limited to, clathrates, zeolites, and cyclodextrins. Each of the colorant and ultraviolet radiation transorber or modified photoreactor or arylketoalkene stabilizing compound can be associated with one or more molecular includant. The includant can have multiple radiation transorbers associated therewith (see co-pending U.S. patent application Ser. No. 08/359,670). In other embodiments, the includant can have many modified photoreactors or arylketoalkene stabilizing compounds associated therewith.
In some embodiments, the colorant is at least partially included within a cavity of the molecular includant and the ultraviolet radiation transorber or modified photoreactor or arylketoalkene stabilizer is associated with the molecular includant outside of the cavity. In some embodiments, the ultraviolet radiation transorber or modified photoreactor or arylketoalkene stabilizer is covalently coupled to the outside of the molecular includant.
The present invention also relates to a method of mutating the colorant associated with the composition of the present invention. The method comprises irradiating a composition containing a mutable colorant and an ultraviolet radiation transorber with ultraviolet radiation at a dosage level sufficient to mutate the colorant. As stated above, in some embodiments the composition further includes a molecular includant. In another embodiment, the composition is applied to a substrate before being irradiated with ultraviolet radiation. It is desirable that the mutated colorant is stable.
The present invention is also related to a substrate having an image thereon that is formed by the composition of the present invention. The colorant, in the presence of the radiation transorber or modified photoreactor or arylketoalkene compound, is more stable to sunlight or artificial light. When a molecular includant is included in the composition, the colorant is stabilized by a lower ratio of radiation transorbers to colorant.
The present invention also includes a dry imaging process wherein the imaging process utilizes, for example, the following three mutable colorants: cyan, magenta, and yellow. These mutable colorants can be layered on the substrate or can be mixed together and applied as a single layer. Using, for example, laser technology with three lasers at different wavelengths, an image can be created by selectively xe2x80x9cerasingxe2x80x9d colorants. A further advantage of the present invention is that the remaining colorants are stable when exposed to ordinary light.
The present invention also includes a method of storing data utilizing the mutable colorant on a substrate, such as a disc. The colorant is selectively mutated using a laser at the appropriate wavelength to provide the binary information required for storing the information. The present invention is particularly useful for this purpose because the unmutated colorant is stabilized to ordinary light by the radiation transorber and can be further stabilized by the optionally included molecular includant.
The present invention also includes data processing forms for use with photo-sensing apparatus that detect the presence of indicia at indicia-receiving locations of the form. The data processing forms are composed of a sheet of carrier material and a plurality of indicia-receiving locations on the surface of the sheet. The indicia-receiving locations are defined by a colored composition including a mutable colorant and a radiation transorber. The data processing forms of the present invention are disclosed in co-pending U.S. patent application Ser. No. 08/360,501, which is incorporated herein by reference.
These and other features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments and the appended claims.